This invention relates to sawmill apparatus, and particularly to a method and apparatus for measuring a cant or flitch for edging employing edge scanning.
Many types of sawmills are employed to cut dimension lumber from substantially cylindrical logs. Generally, the first step in cutting a log to produce dimension lumber involves cutting slabs from sides of the log so that the resulting cant has two parallel faces. As the cant is held in end dogs, it is fed through a bandmill, and flitches (or cants) are cut therefrom wherein each flitch has parallel faces joined by two longitudinal side edges. The two longitudinal side edges are so-called wane edges, i.e., they are usually not perpendicular to the main faces of the flitch but are curved and inclined relative to the main faces. The flitches are suitably conveyed longitudinally to a pin stop table where they are advanced in a direction transverse to their length and upon which the flitches are moved transversely under or over scanner means including a plurality of photocell detectors used to create a model of the flitch. From the pin stop table, the flitch is advanced to an edger where one or both waney edges of the flitch are removed by means of a circular saw fed along a path in transverse relative to the direction of feed of the flitches over the pin stop table. Alternatively the flitch is advanced longitudinally into the saw.
In the apparatus described in Pat. No. 4,196,648, employing photocell scanner technology, cants or flitches are desirably oriented on a pin stop table with the wane up so they can be properly viewed. This assumes the wane is easily seen at both edges of the flitch, e.g. wherein the flitch widens away from the scanner so the wane can be viewed from above. However, for flitches cut from large logs it is possible for the wane along at least one edge of the flitch to recede inwardly or negatively behind or under the visible face of the flitch where it cannot be seen by the foregoing type of scanner apparatus. Furthermore, one or both edges may even change from positive wane to negative wane along the length of the flitch and an improper measurement will result.
Moreover, photocell scanners as described in Pat. No. 4,196,648 view a flitch at approximately one foot intervals along the flitch. In order to maximize recovery of lumber from a flitch it would be desirable to provide a more detailed model such that dimensional variations and imperfections will not be missed, for example it would be desirable to measure the cross-section of the flitch at two or three inch intervals. Based on the principles described in Pat. No. 4,196,648, this would require a large number of scanner devices and would add substantially to the expense of acquiring information regarding the configuration of the flitch.
Accurate viewing of the complete length of a flitch with a single detector, e.g. by employing an intervening rotating mirror or the like between the detector and a stationary flitch, can be inaccurate because of long optical distances between parts of a flitch and the scanner. While a flitch or cant can be moved longitudinally relative to a fixed detector, continuously maintaining accurate orientation of the flitch or cant during scanning, followed by accurate reorientation thereof for sawing, can be very difficult mechanically.